The invention relates generally to valves used in fluidic systems, and more specifically to a passive fluid-flow check valve used in such systems.
Passive macroscale check valves are well known in the art to provide fluid flow control based upon a direction of fluid flow in the system. Check valves typically use a ball, poppet, flexible flap or elastic membrane that will seat or block an orifice to stop flow in one direction through the orifice, typically in a xe2x80x98reversexe2x80x99 direction. When pressure is applied to direct flow in an opposite direction, the xe2x80x98forwardxe2x80x99 direction, the object obstructing the orifice is displaced and relatively free flow ensues. Cracking pressure refers to the pressure differential necessary to resume flow in the forward direction by reopening the valve. Check valves have various figures of merit to measure and define the effectiveness of the valve.
There are a very limited number of valves (passive or active) that are available to work in microfluidic systems. The present invention is well suited for microfluidics, but is not limited to, microscale systems. Those existing valves for microfluidics are typically designed for gas-phase check valve operation and are generally limited to operating pressures below 100 psi. Typical reverse leak rates for passive microscale check valves are on the order of a few microliters per minute with ratios of forward/reverse flow rates up to 103-104. Further, most passive microscale valves require significant micromachining and are complex. Most require component assembly and are ill-suited for integration in microfluidic systems having many other components. Many prior art microvalves are constructed in silicon, making them incompatible for many applications.
The present invention provides a simple valve structure that may be incorporated into a wide range of materials and may be close coupled in microfluidic systems. The preferred embodiment of the present invention provides for a movement of a single particle or a bed of particles to different regions of a valve to present different hydrodynamic resistances, which provide a differential flow resistance.
In one preferred embodiment, a check valve for a fluidic system includes a fluidic conduit having an inlet with a first particle barrier, an outlet with a second particle barrier and a fluid chamber between the inlet and the outlet; and at least one particle disposed in the fluid chamber, the particle(s) aggregating at the first particle barrier to form a first hydrodynamic resistance when a first fluid pressure at the inlet is less than a second fluid pressure at the outlet, the particle(s) aggregating at the second particle barrier to form a second hydrodynamic resistance when the first fluid pressure is greater than the second fluid pressure.
It is another preferred embodiment to provide a method of operating a check valve in a fluidic system. The method includes the steps of aggregating at least one particle disposed in a fluidic conduit at a first particle barrier at an inlet to form a first hydrodynamic resistance in response to a positive pressure differential between an outlet of the fluidic conduit and the inlet to substantially inhibit fluid flow out of the conduit through the inlet; and aggregating the particle(s) at a second particle barrier at the outlet to form a second hydrodynamic resistance in response to a positive pressure differential between the inlet and the outlet to substantially not interfere with fluid flow out of the conduit through the outlet.
The particles may be of varying shapes, sizes and compositions that may facilitate the fabrication and modify the performance of the valve.
The novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.
The preferred embodiments of this invention, illustrating all their features, will now be discussed in detail. These embodiments depict the novel and nonobvious check valve apparatus of this invention shown in the accompanying drawings, which are included for illustrative purposes only. These drawings include the following figures, with like numerals indicating like parts.